1. Field of the Invention
The present invention relates to a light guide plate serving as a planar light-emitting device disposed at the back of a transmissive or semitransmitting reflective liquid crystal display panel and also relates to a backlight unit using the light guide plate.
2. Description of the Related Arts
A backlight unit for a liquid crystal display panel is disclosed, for example, in Japanese Patent Application Publication No. Hei 2-17. This backlight unit includes a tabular light guide plate having an elongated rectangular light entrance surface and a light exit surface extending at right angles to the light entrance surface, and a cold-cathode tube provided along the light entrance surface as a linear light source. In the light guide plate, light from the cold-cathode tube is received through the light entrance surface and emitted from the light exit surface.
There has also been developed a backlight unit having a light guide plate similar to the above and using as a light source a plurality of light-emitting diodes disposed along the light entrance surface of the light guide plate (for example, see Japanese Patent Application Publication No. 2005-317474).
Light-emitting diodes consume less electric power than cold-cathode tubes. Accordingly, the latter backlight unit is superior to the former in terms of electric power consumption. As shown in FIG. 8, however, light-emitting diodes 18 are spaced from each other in the width direction W of a light entrance surface 12a of a light guide plate 12 at a pitch P. Therefore, light cannot sufficiently reach a region on the light guide plate 12 corresponding to a space between each pair of adjacent light-emitting diodes 18, and this region is likely to become dark. This problem may be solved by reducing the pitch P between the light-emitting diodes 18, for example. Although if the light-emitting diode pitch P is reduced, the above-stated problems will be solved, it becomes impossible for sufficient light to reach regions around two opposite side surfaces 12c of the light guide plate 12 near the light-emitting diodes 18. Consequently, the hatched regions of the light guide plate 12 in FIG. 18 appear dark unfavorably.